Galaxies in the thick of it grow up fast

Galaxies living cheek by jowl with others mature faster than those living in less crowded circumstances, the AAO's Dr Amanda Bauer has found.

Dr Bauer, an ARC Super Science Fellow, and her colleagues have been closely studying a distant cluster of galaxies, XMMU J2235.3-2557, with the 8-m Gemini North telescope in Hawaii. They have discovered dozens of previously unknown galaxies in the cluster, which lies 11 billion light-years away. "Such clusters of galaxies are the largest structures in the Universe held together by gravity, and are some of the first systems that formed after the Big Bang," Dr Bauer said. "We have only recently become able to study them in detail, using a special filter that picks out a particular wavelength of light coming from hydrogen gas." Dr Bauer's team has found that the galaxies in the central parts of the cluster stop making stars earlier than do the galaxies on the cluster's outskirts. The central galaxies are swimming in a sea of gas that is very thin but also very hot, up to 100 million degrees Celsius. "This hot gas seems to somehow put the brakes on star formation," Dr Bauer said. To understand better how these crowded environments can boost and then end the growth of galaxies, Dr Bauer and her colleagues are embarking on an Australian-based project to find new galaxies with different levels of isolation. The astronomers will combine existing data with observations from large telescopes in Hawaii and Chile, and the Hubble Space Telescope. They hope their results will help them understand how our Galaxy developed, and how it will interact in future with its nearest neighbours, the Andromeda galaxy and two smaller galaxies, the Magellanic Clouds. All these galaxies will eventually collide and merge. "The current prediction is that this will happen in several billion years," Dr Bauer said. "Our research should tell us how long the resulting galactic system will form new stars before it settles into maturity." Amanda Bauer is one of 12 early-career scientists presenting their research to the public for the first time through Fresh Science, a national program sponsored by the Australian Government.